#include <stdio.h>
#include <math.h>
struct point{
    int x;
    int y;
};
int main()
{
    double dis;
    struct point p1,p2;
    scanf("%d %d %d %d",&p1.x,&p1.y,&p2.x,&p2.y);
    dis=sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));
    printf("%.2lf",dis);
    
    
    
    return 0;
}
